My daughter has an area on her right shoulder that looks like a bunch of burst capillaries or petechiae, i dont really know. it is under the skin...

?? Bruise: If this is a new finding and is localized to just the shoulder, it may well be a bruise or a brush burn and it is fine to watch it for a few days to see if it resolves. Kids sometimes cause a suction bruise by cupping a bottle or cup to the skin, or sometimes by twisting an item of clothing. Petechiae or other unexplained bruises should be evaluated for platelet deficiency or other causes.